In the pulp and paper industry major efforts are made to reduce the use of chemicals in delignification and bleaching processes, since such chemicals, and especially organic chlorine compounds, in the effluent from bleach plants, give rise to environmental pollution.
One approach to reduce the use of chemicals in pulping and bleaching has been concerned with the use of lignin-degrading microorganisms. Lignin-degrading or lignin-modifying enzymes have also been suggested. A comprehensive review of lignin biodegradation has been published in Critical Reviews.RTM. in Biotechnology, Vol. 6, Issue 1, 1987, pp. 1-60, Ed. Stewart, G. G. and Russell, I., CRC Press, Inc. Boca Raton, Fla.
Another approach has been concerned with removal of lignin by using hemicellulases to break hemicellulose bonds. A review article entitled "Hemicellulases: Their Occurrence, Purification, Properties, and Mode of Action," by Dekker, R. F. H. and Richards, G. N. has been published in Advances in Carbohydrate Chemistry and Biochemistry, Vol. 32, 1976, pp. 277-352.
Among the hemicellulases, xylanases are the ones that have attracted most attention for use in biopulping and biobleaching. FR 2 557 894-A1 discloses treatment of paper pulp with an enzymatic solution which does not have any cellulase activity and which contains xylanase. The treatment is effected at 20.degree.-60.degree. C., especially 40.degree. C., and Example 6 reveals that the pH should be 5. However, the paper and pulp industry would be interested in treating wood pulp at higher temperatures and higher pHs for economical reasons and convenience, since some established bleaching processes are conducted at temperatures exceeding 65.degree. C. and pH exceeding 9.
International patent publication number WO 91/18976 discloses .alpha.-L-arabinofuranosidase obtained from B. stearothermophilus. However, the molecular weight data for .alpha.-L-arabinofuranosidase is not disclosed and it would appear that different strains of B. stearothermophilus were used. More particularly, WO 91/18976 discloses the molecular weight ranges for xylanase obtained from B stearothermophilus as 18000-38000, whereas the molecular weight of the xylanase obtained by applicants is 4 1000 to 42000.
To our knowledge, no one has reported treatment of wood pulp with a preparation exhibiting enzymatic activity and having the capability of delignifying wood pulp at a temperature of at least 65.degree. C. and a pH of at least 9.